Floating blade shrouds



March 8, 1960 R. L. WARDLE FLOATING BLADE SHROUDS Filed Oct. 2. 1957 2Sheet-Sheet 1 I4 3 as 24 2a m 21 2 w 2| 2o 26 25 ATTORNYS.

March 8, 1966 R. L. WARDLE 2,921,724

FLOATING BLADE SHROUDS Filed Oct. 2, 1957 2 Sheets-Sheet 2 III.

INVENTOK/ ATTOR EYS 2,927,724; FLOATING BLADE ,SHROUDS Robert Lionelwardleydeceased, late of Brampton, On-

tario, Canada, by Phyllis May 'Wardle, executrix, Brampton, Ontario,Canada, assignor to ,Avro Aircraft Lnmted, Malton, Ontario, CanadaApplication October 2, 1957, Serial No. 687,788

11 Claims. (Cl. 230- 120) This invention relates to seals for theblading of rotary machines of the class comprising turbines,compressors,

blowers and the like and moreparticularly to seals for the blading ofcompressors of gas turbine engines.

Most conventional seals for compressor blading require the provision ofshrouds opposite the blade tips which rotate relatively thereto. Inorder to provide an adequate seal it is necessary that close runningclearances between the blade tips and theshroud be maintained, and thisheretofore could be effected only by costly and timeconsuming machiningprocesses. Furthermore, as a result ofternperature changes within theengines and changing loads imposed by aircraft manoeuvres, the closerunning tolerances required to provide adequate seals are sometimesinsufficient to prevent damage to the blades due to contact with theshrouds.

A proposal which heretofore has been made to alleviate theaforementioned problem is that abrasive surfaces be provided on theshrouds to grind off the blade tips without generating excessive heatand without causing damage. Also, in some instances,,segmental and evenflexible shrouds have been constructed. However, none of these prior artshrouds automatically adjusts itself to variable running clearances. Ina typical prior art flexible shroud construction, as exemplified by thearrangement disclosed in Hardigg United States Patent No. 2,634,090, theshroud is prevented by stops from approaching the blade closer than apredetermined distance. Such constructions sufier from the defect thatthe clearances between the blades and the shrouds are much greater thanis desirable;

furthermore, accurate machining of the blade tips and of the shrouds andtheir stops still is required.

It is an object, therefore,'of this invention to provide effective andyet economical flexiblesealing means between the blade tips and theopposed relatively rotatable member in rotary compressors, turbines,blowers and the like.

United States Patent It is another object of the, invention ,to provideflexible sponding parts throughout the several views, and in which:

Fig. 1 is a side elevation of a typical axial flow gas turbine engine inwhich the invention is embodied;

Fig. 2 is an. enlarged fragmentary radial section through the compressorof the engine of Fig. 1; and showing particularly two embodiments ofsealing devices constructed.

in accordance with the invention. a

Fig. 3 is a section taken through the line 33 of Fig. 2;

Fig; 4 is a fragmentary section similar to Fig. 2, but

'the stator member 14, the stator blades 2.8,; described in detailhereinafter. I

The portion of the stator member opposed to the shroud.

, 2 showing another embodiment of a sealing device constructed inaccordance with the invention;

Figs. 5, 6 and '7 are perspective views of various types of segmentallaminar rings constructed in accordance with the invention. I

An axial flow gas turbine engine 10, as shown in 1;

comprises a compressor 11 inwhich air is compressed and passed to acombustion system 12 where it is mixed with fueland'burned to form gasesof high temperature. The gases are then expanded through a turbine 13,which drives the compressor 11, and they are discharged rearwardly toprovide a propulsive thrust.

The inventionwill be described as'embodied in a com- Presser of a gasturbine engine, but it will be evident that J I the invention is equallyadaptable for use with the turbine of such engines and in fact'with anyrotary machines of I ber 14 and a rotor member 15 .between which is anannular passage, and rings of blades of aerofoil section with theirlongitudinal axes radially disposed relative to the axis of rotation; ofthe rotor member in the annular passage. Alternate' rings comprisestator blades 16 having root ends 17 secured to thestator member 14 andtheir other ends extending toward the rotor member 15,

while the other rings comprise rotor blades 18 having their root endssecured to the rotor member 15 and their outer ends extendingtowards thestator member 14. The blades may be secured to, the stator member ortothe rotor member by any conventional means. 1

1 In the engine illustrated in the drawings the flow of air is from.right to left. As the air flows through the compressor thereis a gradualincrease in the pressure do to the work performed on the air by therotating blades, and 1 thus the, pressure on the downstream side of ablade ring is higher than the pressure on its upstream.side.- The airconstantly. tries to escape from the high pressure.

side tothe low pressure side through the clearance between the tips ofthe blades and the opposed member.

A preferred embodiment of the invention for minimizing this escape ofair is shown in Figs. 2 and 3 of the drawrings will first be describedindetail.

and encircling. them is an annular shroud 19 which is spaced from theopposed member, that is from the stator member 14 in this case. Therotor assembly therefore comprises the rotor member 15, the rotor blades18 and the shroud 19; Similarly-the stator assembly comprises 16 and ashroud f.) can be considered as a channel provided by'longitudin alcircumferential wali 2b which is generally perpendicular to thelongitudinal asset the blades and spaced from the tips of the blades,and bytransverse circumferential walls 21 and 2.2 which aresubstantially,perpendicular to the longitudinal wall and spaced from theedges of the blades and ofthe shroud. in the space betweenthe wall 20and the shroud l i is a laminar ring '23 secured atone edge in acircumferential slot machined in the wall 22, and which allows freemovement of the ring in an axial direction while restricting movementor" the secured edge in a radial direction. The ring 23 inherently isflexible and therefore in effect it is hingedly mounted on the wall 22.

Preferably each laminar ring 23 comprises a plurality S sta s- M 1960-ings. The sealing device for one of the rotor blade of segments eachhaving a radius of curvature equal to that of the slot in the wall 22 inwhich it is placed and a circumferential length of about 3 inches. Thesegments are arranged in end to end abutting relationship so thattogether they form a substantially continuous ring. At the free edge ofthering 23 is a lip 24 which is in substantially sealing contact withthe wall 21 and is'slidable relative thereto.

Small holes 25 (say, ,6, inch in diameter) are drilled in the ring 23adjacent its hinged edge and are circumferentially spaced from eachother by approximately one inch. These holes provide means which connectthe chamber 26 defined by the walls 20, 21 and 22 and by the ring 23 tothe fluid at the upstream or low pressure side of the blades, and thusprevent a build up of pressure in the said chamber which would otherwiseoccur due to any leakage of fluid between the lip 24 and the wall 21from the high pressure side of the blade ring.

The face of the ring 23 which is opposed to the shroud 19 definestherewith a diverging passage 27. Any flow of air between the ring andthe shroud will be from the high pressure side to the low pressure side;thus, the passage diverges downstreamly in the sense of the fluid flowtherethrough.

The functioning of the sealing device of the invention is based on thefact that air drops in pressure when it accelerates through a passage,thus creating a suction on the walls which constitute the passage. Sinceone wall of the passage, namely the ring 23, is free to move, the gapbetween the shroud and the ring will vary to establish equilibriumbetween the suction forces on one side of the ring and the forces in theopposite direction; in other words the gap will narrow to an extent suchthat the forces balance each other.

It will be noted that the small amount of air which leaks through thegap between the shroud and the ring must first scrub against the lip 24of the ring and be deflected thereby by approximately 90. The force ofthe air applied against the lip as the air is deflected by the lipconstantly will urge the lip into engagement with the wall 21 and thelip thus forms a substantially airtight seal with the wall 21. However,as mentioned previously, the holes 25 allow any air that might leakbetween the wall 21 and the lip 24 to escape into the relatively lowpressure region at the upstream side of the blade ring, thus preventinga build-up of pressure in the chamber 26. This will mean, of course,that the pressure in the chamber 26 is substantially the same as thepressure at the upstream side of the blade ring and therefore, thetilting movement of the ring 23 is governed by the flow of air in thediverging passage 27 between the shroud 19 and the ring 23. That is, asthe gap widens the pressure drops 1n the diverging passage 27 and thering is urged towards the shroud 19 by the pressure in the chamber 26.The ring cannot touch the shroud because of the existing pressureconditions, and the ring will tend to take up a position so that thepressure in the diverging passage 27 balances the pressure in thechamber 26.

The above-described functioning of the ring 23 occurs as described, eventhough there may be slight fluctuations in pressure in the chamber 26.As leakage air flows along diverging passage 27, its static pressureincreases but it is to be remembered that the static pressure exerted bythe high velocity stream in the throat or narrowest part of theconverging passage 27 is extremely low and the increase therein due todivergence of the passageway is not sufiicient to produce a real highpressure zone at the exit of the passage. While the pressure atthatpoint may be slightly above the inlet pressure to the blade, it will notraise the pressure in chamber 26 very much above that inlet pressureeven though it is transmitted through opening 25. The actual pressuresexisting in the diverging passage depend upon the quantity of airflowing therein. If that pressure becomes too high and increases thepressure in chamber 26, through opening 25, the effect 4 will be to flexring 23 to further restrict passage 27 and thus reduce the quantity ofair flowing with a consequent reduction in static pressure in the regionof the openings 25. It is to be further remembered that air dischargingfrom the passage 27 immediately drops to a pressure equal to the inletpressure referred to. a

The sealing ring illustrated in the lower part of Fig. 2 is in onerespect an inversion of the construction previously described. Extendingaround the tips of one ring of the stator blades 16 is an annularchannel section shroud generally indicated at 28 and which includes aweb 29 secured to the blades and annular flanges 30 and 31. A laminarring 32 is hinged at one edge to the flange 31, and the other edge ofthe ring is in sliding engagement with the flange 30 and is insubstantial sealing contact therewith. One resilient plastic substancewhich has been used successfully for the ring 32 is manufactured by E.I. du Pont de Nemours & Company, Inc., and is sold under the trademarkTeflon. It is a substance which will withstand temperatures of the orderof 500 C. and still remain resilient.

A diverging passage 33 is defined by the rotor 15 and by a portion ofthe ring 32. Between the ring 32 and the web 29 is a chamber 34 which ismaintained at the relatively low pressure of the upstream side of theblade ring by the provision of holes 35 which are perforated in theshroud 28. In operation, the ring 32 is similar to the operation of thering 23 previously described.

The embodiment of the invention illustrated in Fig. 4 is similar in allrespects except one to the embodiment previously described withreference to the upper part of Fig. 2.

There is attached to the face of laminar ring 36, a rubbing strip 37 ofany suitable plastic substance having the required characteristics ofdurability and of resistance to high temperatures. I

The rubbing strip assures that the ring 36 suffers no damage should itunder'some conditions, especially at starting and stopping of theengine, contact shroud 38. A substance which has been used successfullyfor the rubbing strip 37 is that sold under the trademark Teflon" andmentioned above. The Teflon may be bonded to the ring as a strip, or therequired thickness of approximately 0.020 inch may be built up byspraying. It may be advantageous to impregnate the Teflon with graphitein order to reduce its co-eflicient of friction.

In Fig. 5 is illustrated the preferred form of segmental laminar ring23. An alternative segmental laminar ring 23a illustrated in Fig. '6 isprovided at its longitudinal edges with flanges 23b which act asstiffeners to prevent warpage due to uneven temperature distribution.

It may also be desirable to construct rings having longercircumferential lengths than those previously described. In such a casethe material thickness could be substantially reduced by providingstiffening ribs 39 evenly spaced circumferentially and disposed parallelto the engine axis, as illustrated in Fig. 7.

It will be understood that the form of the invention herewith shown anddescribed is a preferred example and various modifications can becarried out without departing from the spirit of the invention or thescope of the appended claims.

What is claimed is:

V 1. A rotary machine, of the class comprising turbines. compressors,blowers and the like, including a stator assembly, a rotor assemblyrotatably mounted in the stator assembly, said assemblies including arotor member, a stator member, blades rooted at one end in one of themembers with their tips or other ends opposite a generally cylindricalportion of the other member but spaced therefrom, an annular shroudsecured to the blade tips and spaced from said portion of the othermember, and a sealing device for preventing a substantial leakage offluid between the tips of the blades and said portion of theQthenmemher'from the high pressure side to the relati'vely lowerpressure side; the sealing device comprising a laminar ring in the spacebetweenthe shroud and said portion of the other member, means at oneedge of the ring to hingedly secure the ring to the stator assembly inspaced relationship to the opposed portion of the rotor assembly andenabling the ring to tilt, the face of the ring which is opposed to therotor assembly being angularly related to the opposed portion of'therotor assembly and thereby defining therewith a passage which divergesdownstreamly in the sense of the fluid flow through the passage, theother edge of the ring being in substantial sealing contact with thestator assembly and being slidable relative thereto, the other face orthe ring and the s e b y a d n b n h has o tilt, he te fy h live to therotor assembly.

2. A rotary machine, of the class comprising turbines, I

compressors, blowers and the like, including a stator assembly, a rotorassembly rotatably mounted in the stator assembly, said assembliesincluding a rotor member, a stator member, blades rooted at one end inone of the members with their tips or other ends opposite a generallycylindrical portion of the other member but spaced therefrom, an annularshroud secured to the blade tips and spaced from said portion of theother member, and a sealing device for preventing a substantial leakageof fluid between the tips of the blades and said portion of the othermember from the high pressure side to the relatively lower pressureside; the sealing device comprising a plurality of laminar segmentsarranged in end to end relationship and which together provide a laminarring in the space between the shroud and said portion of thebthermember, means at one edge of the ring to hingedly secure the ring to thestator assembly in spaced relationship to the opposed portion ofthe'rotor assembly and enabling the ring to tilt, the face of the ringwhich is opposed to the rotor assembly being angularly related to theopposed portion of the rotor assembly and thereby defining therewith apassage which diverges downstreamring which is opposed to therotor-assembly being angularly. related to the opposed portion of therotor assembly and thereby defining therewith a passage which divergesdownstreamly in the sense of the fluid flow through theg passage, theother edge of the ring being in substantial sealing contact with thestator assembly and being slidable relative thereto, the other face ofthe ring and the 1 opposed portion of the stator assembly being spaced,apart and, together with the hinged edge and the slidable defining achamber, and ports in the ring adjacent its hinged edge to connect thechamber to the fluid at the low pressure side of the blades, the fluidflow through the diverging passage causing the pressure in the passageto drop to a value less than the pressure in the chamber, the relativepressureslin the passage andjin the chamber tilting the ring to aposition of optimumproxirnity rela- 4. A rotary machine; of the classcomprising turbines, compressors, blowers and the like, including astator member, a rotor member rotatably mounted in the stator member,blades rootedffat one end in the 'rotor'rnember with their tips or otherends opposite a generally cylindrical portion of the stator member butspaced there from, an annular shroud secured to, the blade 'tips andspaced from said portion of the stator member, and a sealing device forpreventing a substantial leakage of fluid between the tips of the bladesand the stator member from the high pressure side to the relativelylower pressure side; the sealing device comprising a laminar ring inthespace between the shroud and the stator member, means at one edge of thering to hingedly'secure the ring to the stator member in spacedrelationship to the opposed, portion of the shroud and enabling the ringto tilt, the face of the ring which is opposed to the shroud beingangularly related to the opposed portion of the shroud and thereby thestatormernber being spaced apart and, together the hinged edge and theslidable edge, defining a chamber,

, and means connecting the chamber tothefiuid at the ly in the sense ofthe fluid flow through the passage, the

other edge of the ring being in substantial sealing contact with thestator assembly and being slidable relative thereto, the other face ofthe ring and the opposed portion of the stator assembly being spacedapart and, together with the hinged edge and the slidabie edge, defininga chamber, and means'connecting the chamber to the fluid at the lowpressure side of the blades, the fluid flow through the divergingpassage causing the pressure in the passage to drop to a value less thanthe pressure in the chamber, the

relative pressures in the passage and in the chamber tilting the ring toa position of optimum proximity relative to tli e rotor assembly.

3. A rotaryimachine, of the class comprising turbines,

compressors, blowers and the like, including a stator assembly, a rotorvassembly rotatably mounted inthe stator assembly, said assembliesincluding a rotor member, a stator member, blades rooted at one endinone of the members with their tips or other ends-opposite a generallycylindrical portion of the other member but spaced therefrom, annularshroud secured to the blade tips and spaced from said portion of theother member, and a sealing device for preventing a substantial leakageof fluid between the tips of the blades and said portion of the othermember from the high pressure side to the relatively lower pressureside; the sealing device comprising a laminar ring in the space betweenthe shroud and the said portion of the other member, means atone edge ofthering to hingedly secure the ring to the stator assembly in spacedrelationship to the opposed portion of the rotor low pressure side ofthe blades, the fluid flow through the a v diverging passage causing thepressure in the passage to drop to a value less than the pressure in thechamber, the

relative pressures in the passage and in the chamber tiltmg the ring toa position of optimum proximity of its said other edge relative to theshroud.

- 5 .-A rotary machine, of the class comprising turbines, compressors,blowers and the like including a stator member, a rotor member'rotatably mounted in the-stator member, blades rooted at one end intherotor member with their tips or other ends opposite a generallycylindrical portion of the stator member but spaced therefrom,

an annular sln'oud secured to the blade tips and spaced from saidportion of the stator member, and a sealing device for preventing asubstantial leakage of fluid be:

tween the tips of the blades and the-stator member from the highpressure side to the relatively lower pressure side; the sealing devicecomprising a laminar ring in; the

space between the shroud and the stator member, means I at one edge ofthe'ring to hingedly secure the ring to the stator member in spacedrelationship to the opposedpor- 1 7 tion of the shroud and enabling thering to tilt, the Iface I oi the ring which is opposed to the shroudbeing angularly, related to the opposed portion of the shroud andthereby" defining therewith a passage which diverges downstrearnly inthe sense of the fluid flow through'the passage, the other edge of thering being in substantial sealingcontactwith the stator member and beingslidablerelativethereto, t i the other face of the ring and the opposedportion of the stator member being spaced apart and, together with andports in the ring adjacent its hinged edge to connect the chamber to thefluid at the low pressure side of the blades, the fluid flow through thediverging passage causing the pressure in the passage to drop to a valueless than the pressure in the chamber, the relative pressures in thepassage and in the chamber tilting the ring to a position of optimumproximity of its said other edge relative to the shroud.

6. A rotary machine, of the class comprising turbines, compressors,blowers and the like, including a stator member, a rotor memberrotatably mounted in the stator member, blades rooted at one end in therotor member with their tips or other ends opposite a generallycylindrical portion of the stator member but spaced therefrom, anannular shroud secured to the blade tips and spaced from said portion ofthe stator member, and a sealing device for preventing a substantialleakage of fluid be tween the tips of the blades and the stator memberfrom the high pressure side to the relatively lower pressure side; thesealing device comprising a laminar ring in the space between the shroudand the stator member, means at one edge of the ring to hingedly securethe ring to the stator member in spaced relationship to the opposedportion of the shroud and enabling the ring to tilt, the face of thering which is opposed to the shroud being angularly related to theopposed portion of the shroud and thereby defining therewith a passagewhich diverges downstreamly in the sense of the fluid flow through thepassage, a lip at the other edge of the ring, the flow of fluid pastsaid lip urging said other edge into substantial sealing contact withthe stator member, the other face of the ring and the opposed portion ofthe stator member being spaced apart and, together with the hinged edgeand the other edge, defining a chamber, and means connecting the chamberto )the fluid at the low pressure side of the blades, the fluid flowthrough the diverging passage causing the pressure in the passage todrop to a value less than the pressure in the chamber, the relativepressures in the passage and in the chamber tilting the ring to aposition of optimum proximity to the shroud.

7. A rotary machine, of the class comprising turbines, compressors,blowers and the like, including a stator member, a rotor memberrotatably mounted in the stator member, blades rooted at one end in therotor member with their tips or other ends opposite a generallycylindrical portion of the stator member but spaced therefrom, anannular shroud secured to the blade tips and spaced from said portion ofthe stator member, the surface of the shroud which faces the statormember being inclined relative thereto so that the space between theshroud and the opposed portion of the stator member is of progressivelyincreasing width from the high pressure side to the relatively lowerpressure side; and a sealing device for preventing a substantial leakageof fluid between the tips of the blades and said portion of the statormember from the high pressure side to the relatively lower pressureside, the sealing device comprising a laminar ring in the space betweenthe shroud and the stator member, means at the edge of the ring which isin the relatively wide part of the aforesaid space to hingedly securethe ring to the stator member in spaced relationship to the opposedportion of the shroud and enabling the ring to tilt, the face of thering which is opposed to the shroud being angularly related to theopposed portion of the shroud and thereby defining therewith a passagewhich diverges downstreamly in the sense of the fluid flow through thepassage, the other edge of the ring being in substantial sealing contactwith the stator member and being slidable relative thereto, the otherface of the ring and the opposed portion of the stator member beingspaced apart and, together with the hinged edge and the slidable edge,defining a chamber, and means connecting the chamber to the fluid at thelow pressure side of the blades, the fluid flow through the divergingpassage causing the pressure in the passage to drop me value less thanthe pressure in the chamber, the

relative pressures in the passage and in the chamber tilting the ring toa position of optimum proximity relative to the shroud.

8. A rotary machine, of the class comprising turbines, compressors,blowers and the like, including a stator member, a rotor memberrotatably mounted in the stator member, blades rooted at one end in thestator member with their tips or other ends opposite a generallycylindrical portion of the rotor member but spaced therefrom, an annularshroud secured to the blade tips and spaced from the said portion of therotor member, and a sealing device for preventing a substantial leakageof fluid between the tips of the blades and said portion of the rotormember from the high pressure side to the relatively lower pressureside; the sealing device comprising a laminar ring in the space betweenthe shroud and the rotor member, means at one edge of the ring tohingedly secure the ring in sealing engagement with the edge of theshroud which is subjected to the relatively lower pressure, the hingingmeans enabling the ring to tilt, the face of the ring opposed to therotor member being angularly related to the opposed portion of the rotormember and thereby defining therewith a passage which divergesdownstreamly in the sense of the fluid flow through the passage, theother edge of the ring being in slidable engagement with the other edgeof the shroud and in substantial sealing contact therewith, the otherface of the ring and the opposed portion of the shroud being spacedapart and, together with the hinged edge and the other edge of the ring,defining a. chamber, and means connecting the chamber to the fluid atthe low pressure side of the blades, the fluid flow through thediverging passage causing the pressure in the passage to drop to a valueless than the pressure in the chamber, the relative pressures in thepassage and in the chamber tilting the ring to a position of optimumproximity rela tive to the rotor member.

9. A rotary machine, of the class comprising turbines, compressors,blowers and the like, including a stator member, a rotor memberrotatably mounted in the stator member, blades rooted at one end in thestator member with their tips or other ends opposite a generallycylindrical portion of the rotor member but spaced therefrom, an annularshroud secured to the blade tips and spaced from the said portion of therotor member, and a sealing device for preventing a substantial leakageof fluid between the tips of the blades and said portion of the rotormember from the high pressure side to the relatively lower pressureside; the sealing device comprising a laminar ring in the space betweenthe shroud and the rotor member, means at one edge of the ring tohingedly secure the ring in sealing engagement with the edge of theshroud which is subjected to the relatively lower pressure, the hingingmeans enabling the ring to tilt, the face of the ring opposed to therotor member being angular-1y related to the opposed portion of therotor member and thereby defining therewith a pas sage which divergesdownstreamly in the sense of the fluid flow through the passage, theother edge of the ring being in slidable engagement with the other edgeof the shroud and in substantial sealing contact therewith, the otherface of the ring and the opposed portion of the shroud being spacedapart and, together with the hinged edge and the other edge of the ring,defining a chamber, and ports in the shroud adjacent to the hinged edgeof the ring to connect the chamber to the fluid at the low pressure sideof the blades, the fluid flow through the diverging passage causing thepressure in the passage to drop to a value less than the pressure in thechamber, the relative pressures in the passage and in the chambertilting the ring to a position of optimum proximity relative to therotor member.

10. A rotary machine, of the class comprising turbines, compressors,blowers and the like, including a stator member, a rotor memberrotatably mounted in the stator member, blades rooted at one end in therotor member,

the stator member including a channel provided by a majorcircumferential wall generally perpendicular to the longitudinal axes ofthe blades and spaced from the tips of the blades and minorcircumferential walls generally normal to the major wall andspaced fromthe edges of the blades, an annular shroud secured to the blade tips andspaced from the channel walls, and a sealing device for preventing asubstantial leakage of fluid between the tips of the blades and thestator member from the high pressure side to the relatively lowerpressure side; the sealing device comprising a laminar ring positionedbetween the shroud and the major channel wall, hinging meansco-operating with the minor channel wall which is subjected to therelatively lower pressure to hingedly secure one edge of the ring sothat the ring is in spaced relationship to the shroud, the said hingingmeans enabling the ring to tilt, the other edge of the ring being insubstantial sealing contact with' the other minor wall of the channeland being slidable relative thereto, the face of the ring which isopposed to the shroud being angularly related to the opposed portion ofthe shroud and thereby defining therewith a passage which divergesdownstreamly in the sense of the fluid flow through the passage, theother face of the ring, together with the channel walls, defining achamber, and means connecting the chamber to the fluid at the lowpressure side of the blades, the fluid flow through the divergingpassage causing the pressure in the passage to drop to a value less thanthe pressure in the chamber, the relative pressures in the passage andin the chamber tilting the ring to a position of optimum proximityrelative to the shroud.

11. A rotary machine, of the class comprising turbines, compressors,blowers and the like, including a stator member, a rotor memberrotatably mounted in the stator member, blades rooted at one end in thestator member with their tips or other ends opposite a generallycylindrical portion of the rotor member but spaced therefrom, and anannular channel-section shroud secured to the blade tips and spaced fromsaid portion of the rotor member, the shroud including a web' whereby itis secured to the-blade tips and having circumferential flanges at eachedge of the web, and a sealing device for preventing a substantialleakage of fluid between vthe tips of the blades and said portion of therotor member from the high pressure side to the relatively lowerpressure side; the sealing device comprising a ring positioned betweenthe channel and the rotor member, the ring being hingedly secured at oneedge to, and in sealing engagement with, the shroud flange which issubjected to the relatively lower pressure, the said hinging meansenabling the ring to tilt, the opposite edge of the ring being insliding engagement with the other channel flange and in substantialsealing contact therewith, the face of the ring which is opposed to therotor member being angularly related to the opposed portion of the rotormemher and thereby defining therewith a passage which divergesdownstreamly in the sense of the fluid flow through the passage, theother face of the ring and the channel defining a chamber, and meansconnecting the chamber to the fluid at the low pressure side of theblades, the fluid which flows through the diverging passage causing thepressure in the passage to drop to a valu less than the pressure in thechamber, the relative pressures in the passage and in the chambertilting the ring to a position of optimum proximity relative to therotor member.

References Cited in the file of this patent UNITED STATES PATENTS2,427,244: Warner Sept. 9, 1947 2,611,532 Ljungstrom Sept. 23, 19522,634,090 Hardigg Apr. 7, 1953 ,FOREIGN PATENTS 852,789 Germany Oct. 20,1952

